Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump

Kirill A. Shutemov
2016-11-25T12:26:30Z

On Tue, Oct 25, 2016 at 09:51:12AM -0500, Josh Poimboeuf wrote:
> Printing kernel text addresses in stack dumps is of questionable value,
> especially now that address randomization is becoming common.
>
> It can be a security issue because it leaks kernel addresses. It also
> affects the usefulness of the stack dump. Linus says:
>
> "I actually spend time cleaning up commit messages in logs, because
> useless data that isn't actually information (random hex numbers) is
> actively detrimental.
>
> It makes commit logs less legible.
>
> It also makes it harder to parse dumps.
>
> It's not useful. That makes it actively bad.
>
> I probably look at more oops reports than most people. I have not
> found the hex numbers useful for the last five years, because they are
> just randomized crap.
>
> The stack content thing just makes code scroll off the screen etc, for
> example."
>
> The only real downside to removing these addresses is that they can be
> used to disambiguate duplicate symbol names. However such cases are
> rare, and the context of the stack dump should be enough to be able to
> figure it out.
>
> There's now a 'faddr2line' script which can be used to convert a
> function address to a file name and line:
>
> $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
> write_sysrq_trigger+0x51/0x60:
> write_sysrq_trigger at drivers/tty/sysrq.c:1098
>
> Or gdb can be used:
>
> $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
> (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).
>
> (But note that when there are duplicate symbol names, gdb will only show
> the first symbol it finds. faddr2line is recommended over gdb because
> it handles duplicates and it also does function size checking.)

The commit breaks scripts/decode_stacktrace.sh.

Not sure if it's possible to fix it only on decode_stacktrace.sh side: we
seems don't have a way to clearly distinguish stack trace line of any
other.

May be we should mark stack lines with some prefix to simplify decoding?

--
Kirill A. Shutemov